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Condensation problem on windows

| Posted in Energy, Heating & Insulation on August 15, 2005 06:44am

I built a house 4 years ago and the homeowners have had a problem with condensation on the windows, in the winter, since they moved in. The house was wrapped with Tyvec, 2×6 studs with fiberglass insulation and 6 mill plastic on walls and 2nd floor ceiling the  attic has about 18 inchs of blown in cellulose. The bathrooms, range and  the dryer are all vented to the outside and they assure me they are using fans. The basement is a superior wall construction, that has been insulated and has 6 mill plastic on the walls. When you walk in the house in the winter you can feel the humidity and a trip to the basement feels much dryer than upstairs, go figure. They only item I did not install was the heating system which is propane hot air and the HVAC guy was a friend of the home owner and is now out of business. The windows are Crestline high effeciency windows. I put alot of effort into the energy detailing as I build in central Pennsyvania, and have used all the same sytems with good results. The fiberglass sales people say I should remove the plastic from the second floor ceiling so the vapor can escape through the drywall ceiling. I wonder if the furnace is so over sized it isn’t running long enough to remove the moisuture. It seems very unusual to me for a hot air system to not make a dry house. Any feed back would be apprciated.

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  1. BryanSayer | Aug 15, 2005 07:59pm | #1

    Do they have a humidifier on the furnace that is either set WAY too high, or is malfunctioning? It should be set between about 30 to 50%.

    Also, what area is the house in? Is winter air dry? If so, it seems to me that the moisture has to be being generated inside the house - that is, it couldn't be the furnace not running enough. Even if it wasn't running enough, the winter air is dry.

    Could you get them to keep a log of their daily activities to see if they are doing something that would cause excess moisture? Like, maybe a tie-dye business? Or do they keep a tropical forest in the house? Plants give off moisture.

    Good luck!

    1. Rickytic | Aug 15, 2005 08:49pm | #2

      Thanks for the response. No, there is no humidifier on the furnace and the only extra moisture maker I saw was a small aquairum. Very few house plants and one 10 year kid. No teenagers taking long showers. It is very strange, when you walk in the house you get hit with the humidity and nobody can explain it. A log sounds like a good idea. Central PA is not so cold that we don't have some humidity in the winter, but I keep telling myself they must be making the moisture. The problem now is the windows are getting black from the condensation and they woant to sue the window people. I keep telling them that is not the problem. Thanks again.

      1. mek | Aug 15, 2005 09:25pm | #3

        Your clients need a seriously smart and licenced HVAC inspection. Tight houses have particular needs for fresh air to the heater and indeed in a very tight house, to a gas stove. There is a possibility that the heater is not venting its own combustion gasses properly, thus putting moisture (and carbon monoxide) into the living space.

  2. AndyEngel | Aug 15, 2005 09:34pm | #4

    Rick, the type of heat doesn't matter in terms of humidity, as long as it's vented and there's no humidifier.

    The question really is where the water is coming from? Is there a vapor barrier below the basement slab? Are you certain that the furnace or water heater aren't back-venting into the house? Plumbing leaks? Just how tight is the house? Are you getting .3 air changes/hour, which is the ASHRAE standard? Have you had a blower door test done? If you did a really good job sealing the poly, you might not be getting the air changes. Then the solution isn't to encourage moisture into the attic (Not a smart solution), but rather to consider an air to air heat exchanger to increase the ventilation.

    Andy Engel

    Senior editor, Fine Woodworking magazine

    An updated profile is a happy profile.

    Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig

    None of this matters in geological time.

    1. Rickytic | Aug 15, 2005 10:21pm | #6

      Andy: first thanks for the response and I want to let you know I have been a subscriber to fine homebuilding since May 1992 and have used it as my buiding information source many times. To answer your first question we did put a vapor barrier under the slab and the basement feels much dryer than the house. I have not done a blower test, we are in a fairly rural and I will try to find someone who does that. Could you explain how the air exchanger would help with the humidity. Thanks again.

      1. RayMoore2G | Aug 15, 2005 10:59pm | #7

        In the winter,  a heat recovery ventilator can remove interior moisture through ventilation without incurring as large a heat loss as opening a window would cause.

        Tell me more about the construction of the basement walls. Did you put poly on the inside face of the studs? Did you use fiberglass insulation in the stud cavities? What is the foundation made of?

        Where is the furnace located and how is it vented?

        Have you checked the dryer vent to confirm that it is not leaking moist air inside the home? Are the bath vents adequate to keeping the mirror mostly fog free while showering?

        I'm looking forward to hearing from you.

        1. Rickytic | Aug 16, 2005 12:50am | #8

          Ray: Thanks for the reply. The basement is a prefab wall system called Superior Wall it is concrete on the outside, 2" of dow board and concrete studs. The whole system sits on a bed of gravel and the slab is poured at the base before it is backfilled. I have used this system for close to 20 years with excellent results. There is 6" ins.in the studs and 6 mill plastic over that. The basement is very dry compared to the rest of the house. The furnace is located in the basement and is a high efficiency gas unit vented outside with PVC Pipe. I have not personaly seen the dryer running but we put the vent in and the dryer and vent are on an outside wall and the Mrs. assure me it is venting. I should check closer on that to be sure but that was one of my first questions to her. As I said in my original message the furnace is something I realy had nothing to do with but it keeps sounding like the next place to check. Thanks again and any more imput would be wellcome.

          1. RayMoore2G | Aug 16, 2005 01:35am | #9

            A couple of things I would question. Did the dryer get connected properly? It should be easy to check that one.

            I just have to say this next one and you can ignore it if you like. I checked out the superior wall system and I could not figure out if the studs are monolithic with the outer skin, but my problem with the whole thing is the poly on the interior of the wall. If moisture enters the wall for whatever reason it has no exit. It can't dry to the outside and it can't dry to the interior. It might work for  a long time or it might fill up with moisture as has happened to countless basements that have had this vapor barrier installed to the interior. I know this is not related to your problem but I would not continue the practice.

            I wish I could be more help. Check into the HRV and blower door testing. There are infrared cameras that can show problems that can't be seen by the naked eye and having one used on the house might find the issue but it might be costly so exhaust other possibilities first. If you want to go that route I'll call the owner of the company that makes them and find out where one is in your area.

          2. User avater
            constantin | Aug 16, 2005 02:10am | #10

            I agree with you, I don't like the look of the superior wall system either. I would feel a lot better if the concrete shell and studs were on the inside of the thermal envelope. The XPS could be glued on with something like the Rub-R-Wall system to assure that the joints keep the water out and to insulate the thing. Belts and Suspenders.Back to the original query, I think it's pretty likely that the home is suffering from a lack of air exchange and a means for the air to get replaced on the inside. From the sounds of it, there is little infiltration (a blower test would settle that) and I wonder how effectively the appliances, etc. in charge of venting stuff outside can actually work given their environment.I would do a blower door test and follow that up with the retrofit of an HRV if the home is shown to be "tight". Said HRV could be tied into the bathroom to go into high-speed mode during and after occupancy (humidistat, timer, or occupancy sensor + timer), yet replace all the air that is expelled with fresh air from the inside. I would also look into how well the furnace/boiler/dryer/stove/etc. are performing and if their fans can expell all the gases to the exterior. You may want to invest in a direct-vent gas water heater, boiler, etc. to ensure that their combustion air needs are met without resorting to interior air or cutting the thermal envelope to pieces.

          3. RayMoore2G | Aug 16, 2005 05:07am | #12

            I didn't say I didn't like the superior wall system. I just don't like poly on the inside of a basement wall. A wall has to be able to dry to one side or the other. Basement walls can't dry to the exterior so you have to let them dry to the interior. I would only use foam insulation in a basement wall.

          4. User avater
            constantin | Aug 16, 2005 07:14am | #13

            I agree that basement walls have to have a means of drying out. IMO, the superior wall system would be better at repelling watter if the insulation was on the outside, consisted of XPS, and spanned the cracks instead of being inline. The insulation alone would pretty much ensure that the water stays out due to the thermal gradient (or so buildingscience makes me believe). The Rub-R-Wall is simply the icing on the cake.

          5. IdahoDon | Aug 16, 2005 02:35am | #11

            The company I worked for back in Wyoming specialized in ICF high-performance houses that were very tight, and on the other end of the price spectrom I've also helped with some very tight habitat houses that have been blower door tested.  In SE Wyoming the wind blows, and blows, and blows so the better houses are as tight as possible. 

            At least for the climate in the higher-elevation rocky mountains it seems that there are some generalities that may be applicable to your situation. 

            First, A significant amount of water can come through slabs and basement walls causing all sorts of problems.  Our slabs and crawl spaces all need effective moisture barriers, even with our relatively dry dirt.  We've also started using moisture barriers around the footers so that all the concrete stays relatively dry, unable to pass mositure onto anything.  This is very easy, cost effective and can effect large surface areas in many houses. 

            Second, even with effective moisture barriers in place to avoid the movement of ground moisture, very tight houses need additional help in order to avoid "stail air".    On the expensive end there are the air-to-air exchangers that are standard issue on the ICF houses that we built.  On the less-expensive end, Habitat has learned through trial and error with very tight houses that it is more cost effective over a 20 year span to simply use Panasonic exhaust fans in the bathrooms that have dual outputs.  These fans run continuously at a lower speed, selected by the owner, that keeps the humidity down without pumping out all the heat and they can also be run like a normal fan during showers or whatnot.  It has been shown conclusively that even the tightest windows and doors will leak enough air to allow a continuously run fan to effectively vent a modern home.  Unfortuantely, thanks to human nature, fans that are loud or that don't have a time delayed shut off aren't used as much as they should be.

            Finally, leaky ductwork, or simply HVAC systems that aren't designed to suck and blow in the right areas, can draw moist air and ground vapors (Radon, other natural off gasing, etc.) from very small openings in the building envelope. 

            My money is on a fairly simple solution for your excess moisture problem.  I'd spend the $200 on a dual use Panasonic fan and see if a little extra air movement clears up the problem.  I should have also mentioned that these fans are very quiet.  If nothing else, your client will have a really good bathroom fan and they can use the constant-on feature during the worst months. 

            Best of luck, Don

             

             

             

      2. AndyEngel | Aug 16, 2005 03:03pm | #14

        Thanks for the good words on the magazine. I read down through these posts, and you've gotten some great input. There's nothing more I can think of to add.

        Oh - One thing. Your local power company might offer energy audits that include a blower door test. Another resource for finding an energy auditor (I know you're talking moisture, not energy, but the two are inextricably related) is http://www.affordablecomfort.org.Andy Engel

        Senior editor, Fine Woodworking magazine

        An updated profile is a happy profile.

        Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig

        None of this matters in geological time.

  3. User avater
    rjw | Aug 15, 2005 09:43pm | #5

    What mek said: a badly vented furnace and/or water heater can put large amounts of moisture into a home, and can be a CO death risk, as well.


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